The present invention relates to an electrophotographic copying material composed of an electrically conducting film base suitable, in particular, for producing a printing form or a printed circuit, and of a photoconductive film composed of photoconductor, high-molecular-weight binder which is soluble or dispersible in aqueousalkaline or alcoholic solution, sensitizer and/or activator and standard additives.
It is known to use photoconductive films composed of monomeric or polymeric organic photoconductors, sensitizers and/or activators and also alkali-soluble binders on suitable film bases for the production of printing forms or printed circuits by electrophotographic means. See, e.g., German Patent 1,117,391, corresponding to British Patent 944,126. The photoconductive films are deposited by suitable coating techniques from solution or by lamination, as described, e.g., in German Offenlegungsschrift 3,024,772 corresponding to U.S. Pat. No. 4,492,747, on a metallic or metallized film base. In this case the high-molecular-weight binder contains groups imparting solubility in alkali, such as acid anhydride, carboxyl, phenol, sulfone, sulfonamide or sulfonimide groups (German Patent 2,322,047, corresponding to U.S. Pat. No. 4,066,453). As binders, special mention is made of copolymers of styrene and maleic anhydride, and phenolic resins or of copolymers of styrene, methacrylic acid or acrylic acid and methacrylic acid esters.
To produce a planographic printing form, the electrophotographic copying material is charged electrostatically, exposed or electrostatically charged in accordance with an image and developed with a toner of a dry or liquid developer. The toner image produced is fixed by heating to 100.degree. to 250.degree. C. and the film is then stripped with an aqueous-alkaline or alcoholic solution, as a result of which the points not covered by the toner are dissolved. A mask for a printed circuit is obtained in an analogous way.
In the production of a printed circuit by electrophotographic means by known processes, the disadvantage is that the films containing the binder which impart solubility in alkali can either not be deposited or laminated at all onto a copper-clad circuit board or can be deposited or laminated only at relatively high temperature. The high temperature makes the laminating process difficult and results in damage to the generally thermo-sensitive photoconductor substances, sensitizers and activators. The photoconductive film loses photosensitivity as a result. Another disadvantage is that the films used for the electrophotographic process containing the known alkali-soluble binders are no longer flexible enough in fairly large film thicknesses of about 30 .mu.m, such as are required for the production of circuit boards. These films have therefore to be handled with extreme care since even a slight bending can result in an undesirable crack formation and the film consequently becomes unusable.
In the production of a printing form or a printed circuit by electrophotographic means, solvents have to be added to the stripper solution to increase the processing rate. These stripper solutions containing solvents have an associated smell which is criticized by some processors since it is troublesome, particularly during the cleaning of the stripping apparatus.
A further disadvantage of the known alkali-soluble binders is the deterioration of the electrophotographic sensitivity which occurs, particularly in the case of large film thickness.